Thermally expandable thermoplastic microspheres comprise a blowing agent encapsulated within a thermoplastic polymer shell. Thermally expandable thermoplastic microspheres are disclosed in, for example U.S. Pat. No. 3,615,972.
Upon heating, the blowing agent evaporates leading to an increase in an internal pressure of the thermally expandable thermoplastic microspheres, at the same time the thermoplastic polymer shell softens resulting in an expansion of the thermally expandable thermoplastic microspheres to form the expanded thermoplastic microspheres. The expanded thermoplastic microspheres have a diameter often at least 2-5 times that of the thermally expandable thermoplastic microspheres.
The thermally expandable thermoplastic microspheres are available as dry free-flowing thermally expandable thermoplastic microspheres or as a slurry of thermally expandable thermoplastic microspheres i.e. where the thermally expandable thermoplastic microspheres are present in a carrier liquid.
The thermally expandable thermoplastic microspheres or the expanded thermoplastic microspheres are utilised in various applications. The thermally expandable thermoplastic microspheres are used, for example, in thermal printing papers, porous ceramics, injection moulding, extrusion of thermoplastic materials, printing inks, paper and board. The expanded thermoplastic microspheres are used for example as a sensitizer in emulsion explosives, liquid based paints, liquid based coatings and various thermosetting materials such as cultured marble, polyester putty and artificial wood. The expanding thermally expandable thermoplastic microspheres and/or the expanded thermoplastic microspheres may also be used in cementitious compositions, for example to impart freeze-thaw durability to cementitious compositions.
Transporting the expanded thermoplastic microspheres may not be commercially viable since the expanded thermoplastic microspheres require significant volume due to their expanded size. Therefore thermally expandable thermoplastic microspheres are transported to the end-user who produces the expanded thermoplastic microspheres on-site from the slurry of thermally expandable thermoplastic microspheres. The thermally expandable thermoplastic microspheres are then expanded to form the expanded thermoplastic microspheres close to or directly into a process for the final application, e.g. any of those mentioned above.
Apparatuses and methods are known in the art for expanding thermally expandable thermoplastic microspheres to form the expanded thermoplastic microspheres.
JP 2005-254213 discloses an apparatus and a method for manufacturing a heat-expanded microcapsule. The apparatus and method use a heating/foaming tube. JP 2005-254213 discloses that a water slurry of heat-expansible microcapsules is force-fed into the heating/foaming tube with high-temperature steam by applying a back pressure exceeding the pressure of the steam. The heat-expansible microcapsules are discharged into air and then expanded.
U.S. Pat. No. 4,513,106 discloses an apparatus and a method to form expanded thermoplastic microspheres from thermally expandable thermoplastic microspheres. U.S. Pat. No. 4,513,106 discloses that steam is introduced into a slurry of thermally expandable thermoplastic microspheres in a pressure zone in an amount sufficient to heat the thermally expandable thermoplastic microspheres and at least partially expand them. The partially expanded thermoplastic microspheres then leave the pressure zone under a pressure drop whereby the microspheres are further expanded and accelerated into a stream with a velocity of at least 1 m/s.
WO 03/051793 discloses a method of manufacturing an explosive by providing thermally expandable microspheres with steam to cause thermal expansion of the microspheres to form wet expanded microspheres.
The apparatuses and methods of JP 2005-254213, U.S. Pat. No. 4,513,106 and WO 03/051793 have drawbacks in that the resulting expanded thermoplastic microspheres stick together and form agglomerates in the apparatus and the final product. Furthermore, the steam or moisture added to the expanded thermoplastic microspheres, as disclosed therein, often leads to incompatibility of moisture in the expanded thermoplastic microspheres and their use in end applications.
Expanded thermoplastic microspheres are good insulators of heat and when manufactured this poses a problem when they are manufactured and stored. The expanded thermoplastic microspheres often continue to expand in storage. Furthermore since the expanded thermoplastic microspheres have a thermoplastic polymer shell, when this shell is hot this causes the expanded thermoplastic microspheres to stick together and form agglomerates during manufacture and/or storage. Agglomerated expanded thermoplastic microspheres are undesirable in applications where uniformly disperse expanded thermoplastic microspheres are required.
It would be desirable to improve the technology of expanding thermally expandable thermoplastic microspheres in a slurry such that agglomeration of manufactured expanded thermoplastic microspheres is avoided providing highly disperse and uniformly expanded thermoplastic microspheres.
It would be desirable to provide an apparatus and a method for expanding thermally expandable thermoplastic microspheres in a slurry without the need to introduce extra water i.e. steam.
It would be desirable to provide an apparatus and a method for expanding thermally expandable thermoplastic microspheres in a slurry that is flexible in respect of which carrier liquid is used in the slurry of thermally expandable thermoplastic microspheres.
It would be desirable to provide an apparatus and a method for expanding microspheres in a slurry that is flexible in respect to a means for heating the slurry of thermally expandable thermoplastic microspheres to form the expanded thermoplastic microspheres.
It would be desirable to provide an apparatus and a method for expanding thermally expandable thermoplastic microspheres in a slurry which avoids agglomeration of the formed expanded thermoplastic microspheres in the apparatus.
It would be desirable to provide an apparatus and a method for expanding thermally expandable thermoplastic microspheres in a slurry that can be used for a broad range of microsphere grades having various expansion temperatures.
It would be desirable to provide an apparatus and a method for expanding thermally expandable thermoplastic microspheres in a slurry which do not continue to expand once they have left an expansion apparatus.
There is a need to provide an apparatus and a method for the expanding thermally expandable thermoplastic microspheres in a slurry which overcomes at least the aforementioned drawbacks.